In an optical disk apparatus that records data to a disk by laser beams of a semiconductor laser or the like or reproduces it, it is necessary to set the power of the laser to the optimum values for recording and reproducing. However, in the semiconductor laser in general, the property of the power of the emitted light for the drive current largely changes due to changes in the temperatures. Thus, a laser power control circuit is mounted to the optical disk apparatus in order to keep the laser power on the information recording medium to a prescribed value through controlling the drive current for the semiconductor laser.
FIG. 33 is a block diagram of a laser power control circuit disclosed in Japanese Unexamined Patent Publication 6-236576. In FIG. 33, a photodetector 12 detects a part of the laser beams emitted from a semiconductor laser 11, and converts it to an electric signal. The output signal of the photodetector 12 is inputted to an arithmetic processing device 13. The arithmetic processing device 13, while referring to the output signal of the photodetector 12, performs arithmetic processing so that the power of the light emitted from the semiconductor laser 11 becomes a prescribed value, and outputs the result of the arithmetic processing to a laser drive circuit 15. The laser drive circuit 15 drives the semiconductor laser 11 in accordance with the output signal of the arithmetic processing device 13 to control the laser power. A recording power setting signal Sp, a recording power setting end signal Se, and a recording-reproducing switching signal Sc are exchanged between a drive controller 16 and the arithmetic processing device 13 to be used as the timings for storing switchover of the respective laser powers in reproducing or recording state, and the result of the arithmetic processing to an external memory device 14. After completing the setting of the recording power, the laser drive circuit 15 performs modulation action in accordance with the recording signal Sr outputted from the drive controller 16, and recording of information is carried out.
The procedure of setting the recording power disclosed in Japanese Unexamined Patent Publication 6-236576 will be described referring to FIG. 34. FIG. 34 is a flowchart showing the action of the drive controller 16. When the recording action is started, the start of a gap section of a given sector is detected firstly (step S151), and the recording power setting signal Sp is set to “H” (step S152). Then, the end of the gap section is detected (step S153), and the recording power setting signal Sp is set to “L” (step S154). The arithmetic processing device 13 performs the recording power setting in the section where the recording power setting signal is “H”. When the recording power setting is completed, the recording power setting end signal Se to be transmitted to the drive controller 16 is set to “H”. The section where the recording power setting end signal Se is not set to “H” indicates that the recording power setting is not completed in a single gap section. Thus, detection of the gap section and action of setting the recording power setting signal Sp to “H” and “L” are repeated until the recording power setting end signal Se turns to “H” (step S155). Upon detecting that the recording power setting end signal Se is “H”, it is checked whether or not it is a recording sector. If it is not a recording sector, it needs to keep waiting until becoming a relevant recording sector (step S156). If it is a recording sector, the start of the recording region is detected (step S157). When the recording sector is started, the recording-reproducing switching signal is set to “H” (step S158), and the recording signal Sr is outputted to the laser drive circuit 15 (step S159). When the end of the recording region is detected (step S160), the recording-reproducing switching signal is set to “L” (step S161). Thereby, the recording power setting action of the drive controller 16 is completed.
The action of the arithmetic processing device 13 at the time of setting the recording power will be described referring to FIG. 35. FIG. 35 is a flowchart showing the action of the arithmetic processing device 13.
Generally, in a technique for recording data to a disk with laser beams, the semiconductor laser 11 is structured so as to output a bottom power and a peak power alternately as the output powers. The arithmetic processing device 13 detects that the recording power setting signal Sp outputted from the drive controller 16 turns to “H” (step S171). When it is detected that the recording power setting signal Sp is “H”, the arithmetic processing device 13 performs bottom power setting (step S172). The bottom power setting is carried out as below. That is, the arithmetic processing device 13: detects the error between the signal of the photodetector 12 obtained in accordance with the output power of the semiconductor laser 11 and the signal set in accordance with the bottom power; amplifies the magnification that is determined in regard to a loop gain of the set bottom power by considering the semiconductor laser 11, the photodetector 12, and the laser drive device 15; and outputs a control amount voltage for equalizing the target values of the output power and the bottom power of the semiconductor laser 11 to the laser drive device 15 in order to control the power of the semiconductor laser 11. Then, the operation result of the bottom power setting is saved in the external memory device 14 (step S173). When the gap section is ended and it is detected that the recording power setting signal Sp has turned to “L” (step S174), the arithmetic processing device 13 switches to the control for the reproducing power (step S175). This bottom power setting can be executed repeatedly. In such a case, it is returned again to the step S171, and started from the step of detecting that the recording power setting signal Sp turns to “H” (step S176). When the bottom power setting is completed, the arithmetic processing device 13 then performs the peak power setting. That is, the arithmetic processing device 13 detects that the recording power setting signal Sp turns to “H” (S177). When detected that the recording power setting signal Sp is “H”, the arithmetic processing device 13 performs the peak power setting (step S178). The peak power setting is carried out as follows. That is, the arithmetic processing device 13: detects the error between the signal of the photodetector 12 obtained in accordance with the output power of the semiconductor laser 11 and the signal set in accordance with the peak power; amplifies the magnification that is determined for a loop gain of the set peak power by considering the semiconductor laser 11, the photodetector 12 and the laser drive device 15; and outputs a control amount voltage for equalizing the target values of the output power and the peak power of the semiconductor laser 11 to the laser drive device 15 in order to control the power of the semiconductor laser 11 (step S179). Then, the operation result of the peak power setting is saved in the external memory device 14. When the gap section is ended and it is detected that the recording power setting signal Sp has turned to “L” (step S180), the recording power setting end signal Se is set to “H”, and it is informed to the drive controller 16 that the recording power setting is completed and it is ready for recording (step S183). This peak power setting can also be executed repeatedly. In such a case, the reproducing power setting is performed once (step S182), and it is then returned to the step S172 to restart from the step of detecting that the recording power setting signal Sp turns to “H”. After detecting that the arithmetic processing device 13 has turned the recording power setting end signal Se to “H”, the drive controller 16 sets the recording-reproducing switching signal to “H” when the current sector is the recording sector (step S158). If it is not a recording sector, the recording-reproducing switching signal is not “H” (step S184). Thus, after performing the reproducing power setting once (step S185), the step S184 is executed again.
When it is detected that the recording-reproducing switching signal is “H” (step S184), the arithmetic processing device 13 retrieves the operation results of the peak power and the bottom power from the external memory device 14 (step S186), and sets the retrieved values as the peak power and the bottom power (step S187). The peak power and the bottom power are maintained in the section where the recording-reproducing switching signal is “H”. The laser powers are modulated between the peak power and the bottom power by the laser drive device 15 in accordance with the output of the recording signal Sr, and recording is executed. When the recording-reproducing switching signal turns to “L” (step S188), the arithmetic processing device 13 sets the recording power setting end signal Se to “L” (step S189), and sets the reproducing power (step S190). Thereby, the action of setting the recording power is completed.
In this manner, stable power setting can be achieved without giving any influence of the fluctuation of the laser powers to the ID section and the recording region. Further, in Japanese Unexamined Patent Publication 6-236576, it is noted that the bottom power setting may be performed in the gap section that is of right before the recording region that is one or more regions before the target recording region (to be recorded). Furthermore, it is also noted that the settings of the bottom power and the peak power may be performed more than once, and the optimum bottom power and peak power may be set based on the mean values thereof. Moreover, it is described that the power setting may not have to be performed by actually radiating the bottom power and the peak power in the gap section, but two or more different powers may be radiated in the two or more gap sections, and the bottom power and the peak power may be set from the result thereof.
For example, when the loaded disk is a DVD-RAM disk, the recording region per sector is 2416 bytes, and the gap section is about 10 sectors. When the semiconductor laser outputs a large emitted light power such as the peak power or the bottom power in a small gap section in relation to the recording region as in this case, following issues are generated. That is, due to fluctuations in the wavelength and the like, a focus error signal that indicates the position shift between the disk recording face and the beam spot detected by the reflected light from the disk, or a tracking error signal that indicates the position shift between the track of the disk and the beam spot, fluctuates to high frequency, thereby instability of the focus servo or the tracking servo is caused. In addition, since the focus servo and the tracking servo are unstable when recording to the recording region right after the gap section, the recording signal becomes deteriorated.
Further, since the focus servo or the tracking servo in the gap section becomes unstable, the detection accuracy of the motor control clock for rotating the disk, which is generated by the reflected light from the disk, is deteriorated. Therefore, the motor servo becomes unstable.
Furthermore, When the disk is rotated at a high speed and an emitted light with large power is outputted continuously in a plurality of gap sections, the focus servo, the tracking servo, and the motor servo become unstable not only in the gap sections but also in the recording region.